Washers for locking purposes are previously known and normally comprise a central hole for a screw shank. Generally there are many different variants of this arrangement. One particular arrangement is a locking washer comprising teeth on one side and cams on the other side. The teeth can in general be described as being, of a shape that enables them to engage with a surface of a screw head, nut or a element to be attached. One possible shape is a leaning pyramidal shape. The teeth extend radially on the locking washer surface. The other side of the known lock washers can have a cam pattern. The cam pattern in general can be described as a sloped wedge surface where the inclination angle of the cams should be larger than the pitch of the thread of the screw. The cam pattern extends radially. These locking washers are used in pairs where the pair is constituted of two equal washers, however applied such that the cams is adjacent each other and the teeth of the corresponding other side of the washers are facing away from each others. Applied in a correct manner and with the proper hardness of the elements to be attached and the washers to lock the screw joint, this configuration provides for a very safe and reliable attachment. Washers of this type is for example described in the document DE 2 413 760.
In another document US 2008/0014046 A1 is also a washer described that is intended to be used in pairs.